What is the degeneracy of the n = 3 level? That is, how many different states are contained in the energy level E_{3}=-E_{0} / 9?
Strategy This is a good opportunity to review the quantum numbers we have been discussing. The energy eigenvalues for atomic hydrogen depend only on the principal quantum number n (in the absence of a magnetic field). For each value of n, there can be n different orbital angular momentum \ell \text { states }(\ell=0,1, \ldots, n-1). For each value of \ell \text {, there are } 2 \ell+1 different magnetic quantum states \left(m_{\ell}=-\ell,-\ell+1, \ldots, 0,1, \ldots,+\ell\right).